Hydraulic passages have traditionally been closed off or plugged by means of either a pipe plug or a JIC (SAE) type plug.
In high pressure applications, the use of "traditional" plugs can present potential problems. Among such problems are the wedge effect of a tapered type plug inserted into a tapered threaded port which induce stresses into the components when tightened. Additionally, the threads of the pipe plug port are exposed to high pressures causing additional stresses to the components. Further, potential leakage at the location of a pipe plug requires the use of a liquid sealant or Teflon tape to insure that the plug/port is leak free. An alternative to the pipe plug is the SAE type plug. This traditional type of plug has straight threads which eliminates the assembly stresses of the pipe plug. It affects sealing by an O-ring in a counter bore in the port above the threads which is compressed by the head of the plug. This arrangement does not alleviate stresses on the threads attributed to fluid pressure.
When a traditional plug is threaded into sealing engagement with a port formed in a softer aluminum housing to seal a passage at high fluid pressure, the additional stresses placed on the threads resulting from the high pressure of the fluid can cause a failure in the softer aluminum threads and result in leakage. In addition, the stresses exerted by a tapered plug on the aluminum housing can physically distort the housing and can cause housing failures. The housing stresses are aggravated in the HEUI application because of adverse temperature effects attributed to engine and fluid heat.
The prior art has recognized the shortcomings attributed to traditional plug/port assemblies and has positioned the seal beneath the threads. In U.S. Pat. No. 5,110,160 to Brozovic, a high pressure coupling is illustrated in FIG. 1 in which a frusto conical metal-to-metal seating surface 1 is sealed by means of O-ring 2. This alleviates the pressure of the fluid acting on the threads of the fitting while reducing the area over which the fluid acts. This prior art sealing arrangement illustrated in FIG. 1 is applied to a prior art plug made available by the assignee of this invention as shown in FIG. 3. Again, frusto conical area 1 provides a metal-to-metal seat for sealing by O-ring 2 in FIG. 3. The frusto conical seating surface is a small area which produces an angular force or stress throughout the housing body containing the port. When the housing is made of a softer material such as encountered in a HEUI application, the housing is adversely stressed and could become distorted if the plug was over torqued.
In FIG. 2 there is illustrated a gas temperature sensor disclosed in U.S. Pat. No. 5,667,305 to Walker. In the sensor of FIG. 2, an elastomer seal 2 is likewise positioned downstream of the threaded engagement to seal a smaller diameter bore 3. The arrangement in FIG. 2, like the prior art illustrated in FIGS. 1 and 3 reduces the sealing area and thus the force attributed to the fluid which would otherwise act on the threaded connection. The seal in FIG. 2 is radially compressed.